Method for manufacturing pitch

ABSTRACT

A METHOD FOR MANUFACTURING PITCH WHICH COMPRISES HEATING A STARTING TAR TO A TEMPERATURE OF 320 TO 470*C. UNDER AN INCREASED PRESSURE OF AT LEAST ONE KG./CM.2 GAUGE TO PRODUCE GAS, OIL AND PITCH AND SEPARATING THE RESULTANT PITCH BY DISTILLATION FROM THE OIL, SAID STARTING TAR BEING AT LEAST ONE SPECIES SELECTED FROM THE GROUP CONSISTING OF (A) COAL TAR HAVING A FLASH POINT OF 30 TO 140*C. AND ABSOLUTE VISCOSITTY OF 20 TO 30% BY WEIGHT OF 0 TO 270*C. AND CONTAINING 5 TO 30&amp; BY WEIGHT OF 0 TO 270*C. FRACTION, AND (B) OIL GAS TAR HAVING A FLASH POINT OF 20 TO 130*C. AND ABSOLUTE VISCOSITY OF 10 TO 500 CENTIPOISES AT 50* C. AND CONTAINING 10 TO 35% BY WEIGHT OF 0 TO 270* C. FRACTION.

United States Patent Office Patented Sept. 10, 1974 3,835,024 METHOD FOR MANUFACTURING PITCH Kozo Ueda, Kyoto, Jitsumi Kimoto, Takarazuka, and Mitsuru Moritake, Suita, Japan, assignors to Osaka Gas Company, Limited, Osaka-shi, Japan No Drawing. Continuation-impart of application Ser. No. 126,356, Mar. 19, 1971, now Patent No. 3,692,663. This application Sept. 11, 1972, Ser. No. 287,828

Int. Cl. C10c 3/02 US. Cl. 20822 8 Claims ABSTRACT OF THE DISCLOSURE A method for manufacturing pitch which comprises heating a starting tar to a temperature of 320 to 470 C. under an increased pressure of at least one kg./cm. gauge to produce gas, oil and pitch and separating the resultant pitch by distillation from the oil, said starting tar being at least one species selected from the group consisting of (a) coal tar having a flash point of 30 to 140 C. and absolute viscosity of 20 to 1000 centipoises at 50 C. and containing 5 to 30% by weight of O to 270 C. fraction, and

(b) oil gas tar having a flash point of 20 to 130 C. and absolute viscosity of to 500 centipoises at 50 C. and containing 10 to 35% by weight of 0 to 270 C. fraction.

This invention relates to a novel method for manufacturing pitch.

This application is a continuationin-part of our copending application Ser. No. 126,356, filed Mar. 19, 1971 and matured into Pat. No. 3,692,663 on Sept. 19, 1972.

In most tar industries, tar is subjected to distillation under atmospheric or reduced pressure to obtain light, middle and heavy fractions for use as industrial materials and a residue is recovered as pitch. Namely, pitch is produced from high-boiling substances contained in the tar, since almost all low-boiling substances contained therein are utilized to obtain oil. The resulting pitch is used as a binder for producing electrodes, as an impregnating agent for baked electrodes and as an additive to coking coal charge for producing coke. However, the pitch produced by such method is not necessarily satisfactory in properties thereof.

The properties of pitch are generally represented by solubility in solvent: pitch is divided into benzene-soluble content and benzene-insoluble content, the benzene-in soluble content further being divided into quinoline-soluble and quinoline-insoluble contents. Pitch obtained by the above distillation method generally has a softening point in excess of 60 C. and contains 7 to by weight of benzene-insoluble content and 3 to 8% by weight of quinoline-insoluble content. With respect to such properties, increase in benzene-insoluble content inevitably results in greater quinoline-in-soluble content. On the contrary, if it is attempted to lower the quinoline-insoluble content, the benzene-insoluble content will also be lowered with increased benzene-soluble content. In many cases, however, the amount of both benzene-insoluble content and quinoline-insoluble content, and the difference between these two amounts are critical factors to determine the properties of pitch. For instance, if it i desired to obtain an electrode having improved properties in strength, density and specific electrical resistance by using pitch as a binding agent, it is required that the pitch have at least 30% by weight of benzene-in-soluble content and low quinoline-insoluble content and that the component (so-called ff-resin) accounting for the diflerence [between (0 the benzene-insoluble content and the quinoline-insoluble content be at least 20% by weight. Notwithstanding this,

it has been difficult to obtain pitch satisfying such requirements by the conventional method, since an attempt to increase the benzene-insoluble content to more than 30% by weight is accompanied by a corresponding increase in the quinoline-insoluble content. Therefore, it has been proposed to improve the properties of pitch by further heating the pitch with or without air-blowing or by heating the pitch to which a certain additive was added, whereby pitch having a softening point of at least 60 C. and containing 20 to 40% by weight of benzeneinsoluble content and 5 to 20% by weight of quinolineinsoluble content can be obtained. Though the pitch thus obtained satisfies the properties determined by the solubility in solvents, it still fails to give electrodes having satisfactory properties. Thus the solubility in solvents is an important but not decisive indication for determining whether or not pitch has properties suitable for electrode binder, and, therefore, the quality of pitch for such binder is to be finally determined through electrode examination.

Moreover, pitch obtained by the conventional method and containing 15 to 20% by weight of benzene-insoluble content and 5 to 8% by weight of quinoline-insoluble content has been used as impregnating agent for baked electrode to improve physical properties. In such case the baked electrode is impregnated with the pitch and further baked. According to the above method, however, satisfactory improvement can not be attained unless the impregnation with pitch and subsequent baking are repeated several times.

Recently, it is further required to provide an electrode having higher mechanical strengths and lower specific electrical resistance and less thermal expansion coefficient than those of the electrodes obtained by using the conventional pitch as binder or as impregnating agent.

An object of the invention is to provide a method for manufacturing pitch which can be effectively used as electrode binder to produce an electrode having higher mechanical strengths and lower specific electrical resistance and less thermal expansion coefiicient than those of the electrodes obtained by using conventional pitch as binder.

Another object of the invention is to provide a method for manufacturing pitch which can be used as impregnating agent for baked electrode and thereby electrode having satisfactorily improved properties can be obtained with less or without repetition of impregnation and baking operations.

Another object of this invention is to provide a process for manufacturing pitch in which amounts of benzeneinsoluble content and quinoline-insoluble content can be controlled individually.

Another object of this invention is to provide a process for treating tars, whereby pitch can be obtained in high yield of at least 60% by weight based on tars without coking difliculties.

These and other objects of the invention will be apparent from the following description.

The process of the present invention comprises heating a starting tar to a temperature of 320 to 470 C. under an increased pressure of at least one kg./cm. gauge to produce gas, oil and pitch and separating the resultant pitch by distillation from the oil, said starting tar being at least one species selected from the group consisting of (a) coal tar having a flash point of 30 to 140 C. and absolute viscosity of 20 to 1000 centipoises at 50 C. and containing 5 to 30% by weight of 0 to 270 C. fraction, and

(b) oil gas tar having a flash point of 20 to C. and absolute viscosity of 10 to 500 centipoises at 50 C. and containing 10 to 35% by weight of 0 to 270 C. fraction.

Throughout the specification and claims the physical properties of the tar and pitch are determined by the following methods:

Softening point C.):

Mercury method set forth in IIS (Japanese Industrial Standard) K 242166.

Flash point C.)

ASTM D92 and D-1310.

In accordance with this invention, tar having the specific characteristics as above is heated under increased pressure, whereby pitch having particular characteristics can be obtained in a high yield. The pitch obtained in accordance with the present invention has a softening point of at least 60 C. and contains 20 to 45% by weight of benzene-insoluble content and 3 to 20% by weight of quinoline-insoluble content. Although increase of the benzene-insoluble content may result in increase of quinoline-insoluble content, the increase is much smaller than is the case with the conventional method. Even Where the benzene-insoluble content exceeds 30% by Weight, at least 23% by weight of the 8resin component can be retained, this showing a particular advantage that the pitch can effectively be used as a binder in producing electrodes. Moreover, the pitch obtained by the present invention not only has the solvent solubility adapted for use as electrode binder but also displays far more excellent binding effect, thereby making it possible to obtain electrodes having markedly improved bending strength, compression strength, specific electrical resistance and thermal expansion coefiicient. Furthermore, when the resultant pitch is employed as an impregnating agent, electrode having satisfactorily improved properties can be obtained with less or Without repetition of impregnation and baking operations. The reason why such excellent pitch can be obtained in accordance with the present invention is presumably attributable to the fact that when the tar Which is used as a starting material and contains a considerable amount of lwboiling substances is subjected to the heat treatment under increased pressure, not only reactive components in high-boiling substances but also those in low-boiling substances are reacted to produce pitch and at the same time the reaction is suitably controlled due to the presence of low-boiling substances in the reaction system in liquid form to reduce the production of quinoline-insoluble content and to prevent excessive increase of the molecular weight of quinolineinsoluble content, whereby the properties of the resultant pitch are effectively improved. Thus the pitch obtained by the present method contains quinoline-insoluble content having relatively lower molecular weight than those in the pitch obtained by the conventional methods. Such rer sult can not be obtained by conventional methods in which tar is first subjected to distillation to recover oil, and the residue from which low-boiling substances have been recovered is employed as a starting material. Further, the pitch obtained by the present invention can be employed for various uses other than electrode binder and impregnating agents for baked electrode,'for example, additives to coking coal charge, etc.

The pitch obtained in the present invention has usually a softening point of at least 60 C. and it can be adjusted over a wide range as desired by varying heat treatment conditions as well as conditions of distillation conducted after the present heat treatment. Generally, the softening point of pitch is in the range of about 60 to 150 0., though it is possible to obtain pitch having a higher softening point of 150 to 300 C.

The oil obtained in the present invention has excellent thermal or catalytic cracking of petroleum. In the inexample, as absorbents for benzene contained in coal gas. Alternatively, the oil can further be subjected to heat-treatment under increased pressure, whereby pitch having peculiar properties can be obtained. For example, when the oil obtained by the present invention is further heated under severer conditions than those in the process of this invention pitch containing a very low quinolineinsoluble content is obtainable.

The tars to be used as a starting material of this invention include coal tar and oil gas tar produced by thermal or catalystic cracking of petroleum. In the invention tars containing low-boiling substances are used as a starting material, so that there is no need to previously subject the tar to distillation as in the conventional method. Coal tar used in the present invention has a flash point of 30 to 140 C. and absolute viscosity of 20 to 1000 centipoises at 50 C. and contains 5 to 30% by weight of 0 to 270 C. fraction. Oil gas tar to be used in the invention has a flash point of 20 to 130 C. and viscosity of 10 to 500 centipoises at 50 C. and contains 10 to 35% by weight of 0 to 270 C. fraction. The coal tar and oil gas tar having the above properties contain considerable amounts of low-boiling substances which make it possible to obtain pitch having improved properties. On the contrary, if the tars containing no or smaller amount of such low-boiling substances are employed, such improved pitch can never be obtained. Thus the flash point, viscosity and amount of 0 to 270 C. fraction of the starting tars are critical in the invention. Particularly preferable coal tars are those having a flash point of 30 to 120 C. and 20 to 200 centipoises at 50 C. Such tars contain 10 to 30% by weight of 0 to 270 C. fraction. Particularly preferable are oil gas tars having a flash point of 20 to C. and absolute viscosity of 10 to 200 centipoises at 50 C. Such tars contain 15 to 35% by weight of 0 to 270 C. fraction. In the invention coal tar and oil gas tar can be used singly or in admixture with each other.

In accordance with the method of the present invention the starting tar is heated to 320 to 470 C. under increased pressure of at least one log/cm. gauge, whereby reactive components in the starting tar are effectively converted to pitch. More specifically, heavy fraction and relatively low-boiling, unstable condensed ring substances undergo condensation polymerization to be converted to pitch, while the reaction is suitably controlled by the low-boiling substances existing in the reaction system in liquid form. During this step, the reaction temperature of 320 to 470 C. is of important significance: a temperature lower than 320 C. fails to eifect the reaction satisfactorily, whereas a temperature in excess of 470 C. gives rise to coking in the reactor. The reaction may preferably be carried out at a temperature of 380 to 430 C. It is required to efiect the reaction in this step under increased pressure, where by the substances to be reacted in the tar can be retained in a liquid phase to insure effective conversion to pitch. Further, the liquid phase in which the reaction occurs contains a considerable amount of low-boiling substances and thereby the reaction is suitably controlled to produce pitch having improved properties. There is a need to avoid treatment under an atmospheric or reduced pressure, because such treatment would allow relatively low-boiling, unstable condensed ring substances to be left unreacted without subjecting the substances to condensation polymerization for conversion to pitch, this not only preventing formation of pitch with good quality but causing coking during the reaction. On the contrary, when the pressure exceeds 20 kg./crn. gauge, better results will not be achieved and troubles will be encountered with apparatus and operation. Suitable pressure for the reaction at this stage is therefore in the range of 3 to 20 kg./cm. gauge. The reaction time may vary over a wide range depending upon the reaction conditions and properties of pitch to be obtained, but usually the reaction is completed in about 1 to 20 hours.

The heat treatment results in the production of gas, oil and pitch. The gas is taken out from the system for use as a fuel source and the resulting mixture of oil and pitch is subjected to distillation for separation. The pitch thus obtained has a softening point of at least 60 C. and containing 20 to 45% by weight of benzene-insoluble content and 3 to 20% by weight of quinoline-insoluble content.

The pitch obtained by the present invention can eifectively be used as a binder for electrode. Through the electrode examination it has been found that the electrode produced by using the present pitch as binder has higher mechanical strengths, such as bending and compressive strengths, lower specific electrical resistance and less thermal expansion coefiicient than those of the electrode prepared from conventional pitch. Such excellent electrode can never be obtained by using conventional pitch as a binder, even if it fulfills the requirement of the solubility in solvents. This fact clearly shows that the properties of the resultant pitch are improved, in accordance with the present invention, due to the presence of a considerable amount of low-boiling substances in the starting tar. The oil obtained by the present process has excellent thermal stability and is used as a good absorbent since unstable components have been converted to pitch by the heat treatment. The method of the invention can be conducted by batch method as well as in continuous manner.

For a better understanding of the invention examples are given below, in which percentages are by weight.

Example 1 Crude coal tar was passed through a wetted-wall tower at 130 C. to remove water contained therein. The dried tar had a flash point of 83 C. and an absolute viscosity at 50 C. to 102.4 cps. and contained 17.1% of a fraction boiling at to 270 C. The tar was placed in an autoclave equipped with a partial condenser and pressure regulator and heated at 400 C. under 9 kg./cm. gauge for hours. The vapor produced was condensed in the partial condenser for refluxing and non-condensed gas was taken out from the system. The tar thus treated was subjected to isothermal flash distillation to separate pitch and oil.

The yields of the pitch, oil and gas thus obtained and the properties of the pitch are shown in Table 1.

TABLE 1 Yields:

Pitch (percent) 64.0 Oil (percent) 35.1 Gas (percent) 0.9 Properties of pitch:

Softening C.) 80.5 Volatile substance (percent) 45.8 Quinoline-insoluble content (percent) 7.2 Benzene-insoluble content (percent) 32.0

Example 2 Dried coal tar the same as in Example 1 was heattreated in the same manner as in Example 1, except that the conditions applied in the heat treatment step were changed as shown in Table 2 below, in which are also disclosed the properties of the pitch obtained.

TABLE 2 Conditions:

Temperature (C.) 360 Pressure (kg./cm. G) 5 Time (hr.) 18 Yields:

Pitch (percent) 55.1 Oil (percent) 44.6 Gas (percent) 0.3 Properties of pitch:

Softening point C.) 76.0 Volatile substance (percent) 48.2 Quinoline-insoluble content (percent) 8.4 Benzene-insoluble content (percent) 35.2

Example 3 Dried coal tar the same as in Example 1 was heattreated in the same manner as in Example 1, except that the conditions applied in the heat treatment step were changed as shown in Table 3 below, in which are also disclosed the properties of the pitch obtained.

Crude oil gas tar was dried in the same manner as in Example 1 to obtain dried tar having a flash point of 71 C. and an absolute viscosity at 50 C. of 28.7 cps. and containing 20.3% of a fraction boiling at 0 to 270 C. The dried tar was then subjected to the heat treatment in the same manner as in Example 1, except that the conditions applied in the heat treatment step were changed as shown in Table 4 below, in which are also shown the properties of the pitch obtained.

TABLE 4 Conditions:

Temperature C.) 385 Pressure (kg/cm. G) 9 Time (hr.) 5 Yields:

Pitch (percent) 59.3 Oil (percent) 39.6 Gas (percent) 0.7 Properties of pitch:

Softening point C.) 79.8 Volatile substance (percent) 47.2 Quinoline-insoluble content (percent) 8.4 Benzene-insoluble content (percent) 34.2

For comparison tar was treated in the following manners:

COMPARISON-I Coal tar the same as in Example 1 was distilled at 310 C. under atmospheric pressure and the residue was further distilled at 345 C. under reduced pressure of 0.85 kg./cm. gauge. Thus pitch and oil were obtained in yields of 54.9% and 45.1% respectively, based on the weight of the starting coal tar used. The properties thereof are shown in Table 5 below.

TABLE 5 Pitch:

Softening point C.) 67 .7 Volatile substance (percent) 50.7 Quinoline-insoluble substance (percent) 4.1 Benzene-insoluble substance (percent) 18.2 Oil:

Specific ga'vity 1.08 Temperature for 20%-distillation C.) 240.5 Temperature for 50%-distillation C.) 325 Temperature for %-distillation C.) 360 COMPARISONII The pitch obtained in Comparison-I was further heated at 400 C. under atmospheric pressure for 5 hours. The properties of the pitch thus obtained are shown in Table 6 below.

TABLE 6 Softening point C.) 82 Quinoline-insoluble content (percent) 17.1 Benzene-insoluble content (percent) 37.0

What we claim is:

1. A method for manufacturing pitch which comprises heating a starting tar to a temperature of 320 to 470 C. under an increased pressure of at least one kg./cm. gauge to produce gas, oil and pitch and separating the resultant pitch by distillation from the oil, said starting tar being at least one species selected from the group consisting of (a) coal tar having a flash point of 30 to 140. C.

and absolute viscosity of 20 to 1-000 centipoises at 50 C. and containing 5 to 30% by weight of 0 to 270 C. fraction, and

(b) oil gas tar having a flash point of 20 to 130 C.

and absolute viscosity of to 500 centipoises at 50 C. and containing 10 to 35% by weight of 0 to 270 C. fraction.

2. The method according to Claim 1, in which said starting tar is coal tar.

3. The method according to Claim 1, in which said starting tar is oil gas tar.

4. The method according to Claim 1, in which said starting tar is a mixture of coal tar and oil gas tar.

5. The method according to Claim 1, in which said tar is a coal tar having a flash point of 30 to 120 C. and an absolute viscosity of 20 to 200 centipoises at 50 C. and containing 10 to 30% by weight of 0 to 270 C. fraction.

6. The method according to Claim 1, in which said tar is an oil gas tar having a flash point of 20 to 110 C. and an absolute viscosity of 10 to 200 centipoises at 50 C. and containing 15 to by weight of 0 to 270 C. fraction.

7. The method according to Claim 1, in which said heat treatment is conducted at a temperature of 380 to 430 C. under an increased pressure of 3 to 20 kgjcm.

gauge.

8. Pitch which has a softening point of at least 60 C. and contains 20 to by weight of benzene-insoluble content and 3 to 20% by weight of quinoline-insoluble content and which is produced by the method claimed in Claim 1.

References Cited FOREIGN PATENTS 628,474 10/1961 Canada 20844 VERONICA OKEEFE, Primary Examiner US. Cl. X.R. 20844 

